Effect of Spatial Proximity on Chromosomal Translocations Chromosomal translocations are a type of genomic rearrangement known to be involved in cancer development and progression, and they involve the exchange of genetic material between two non- homologous chromosomes. In certain cancers, especially leukemias, lymphomas, and sarcomas, specific translocations are recurrent, meaning different patients present with translocations involving the same two loci on the same two chromosomes. This recurrence of certain translocations leads to the hypothesis that certain regions of the genome are more susceptible to rearrangement, likely through a close spatial proximity in the nuclear space. Despite correlative evidence demonstrating close spatial proximity of commonly translocated regions of the genome using, for instance, Fluorescent In-Situ Hybridization (FISH) techniques, the idea that spatial proximity contributes to the formation of chromosomal translocations has not be directly or thoroughly tested. Our laboratory developed a novel genetic system with which we can detect Non-Homologous End- Joining (NHEJ)-mediated reciprocal chromosomal translocations in the S. cerevisiae model organism. This system allows for the simultaneous induction of DNA duplex breaks on separate chromosomes, and the real time detection of reciprocal chromosomal translocations. Additionally, the yeast genome has recently been mapped in three-dimensional space, revealing the patterns of non-random chromosomal territories in the nucleus, with the centromeres clustered near the spindle pole body, the chromosome arms outstretched, and the telomeres tethered to the nuclear membrane. The focus of this proposal is to directly test the idea that spatial proximity contributes to the formation of recurrent chromosomal translocations in two ways. First, using the three-dimensional genome map as a guide, two DNA break-sites will be placed at different locations in the genome, at different spatial distances from each other. The frequency of chromosomal translocation formation will be correlated to the spatial distance, as measure by the Chromosome Conformation Capture (3C) assay. Next, at these specified locations, the chromatin architecture will be modified by changing the cell cycle phase and by deleting factors involved in the telomere-tethering to the nuclear periphery. Spatial proximity and chromosomal translocation frequency will be assessed using the 3C assay and the translocation genetic strain, respectively. This study will shed light on the molecular mechanism leading to chromosomal translocations and set the stage for characterizing the equivalent processes in humans. PUBLIC HEALTH RELEVANCE: The long-term goal of our study is to dissect a molecular mechanism that contributes to chromosomal translocations. Chromosomal translocations are a type of genomic rearrangement involved in cancer development and progression, and the proposed research will characterize how the chromatin architecture may cause susceptibility to this mutagenic process. This research will identify and characterize the mechanisms involved in translocation formation to potentially uncover novel therapeutic strategies aimed at preventing or hindering the formation of genomic rearrangements, such as translocations.